Vegetable IPM Advisory Veg 2024

Beetles on Vegetables

In this Issue

  • Cucurbits: Western Striped and Western Spotted Cucumber Beetles
  • Tomatillos: Three-lined Potato Beetles
  • Potatoes: Colorado Potato Beetles
  • Asparagus: Asparagus and Spotted Asparagus Beetles
  • Sweet Corn: Western Corn Rootworm

Beetles are insects belonging to the order Coleoptera, which encompasses several different families and species. Some of these beetles are currently active and can pose a significant threat to Utah’s vegetable production. These voracious feeders can cause extensive damage to crops, leading to reduced yields and compromised plant health. As beetle populations continue to proliferate in the landscape, farmers and gardeners must implement effective monitoring and control strategies to mitigate their impact.

Western Striped and Western Spotted Cucumber Beetles

Adult western striped cucumber beetles (Acalymma trivittatum) are about 1/3 inch long, with black heads and yellow and black-striped wings. Adult western spotted cucumber beetles (Diabrotica undecimpunctata undecimpunctata) are of similar size, featuring twelve black spots on their yellowish wings. The striped cucumber beetle can be a serious pest of cucurbits in Utah, while the spotted cucumber beetle is a minor pest. Adults of both species feed on leaves, but only the striped beetles feed on the fruits. The larvae are 1/3 to 1/2 inch long, with white to yellowish bodies, brown heads, and three pairs of brown legs. Pupae are about 1/4 inch long and yellowish-white.

The beetles overwinter in protected sites near agricultural fields and home gardens, such as under plant debris or in crevices of buildings, and become active in spring when temperatures exceed 50°F. After mating, females lay 200-1,200 eggs in moist soil at the base of cucurbit plants, with larvae initially feeding on roots before moving to the rinds and flesh of cucurbit fruits. In addition to direct feeding injury, cucumber beetles can vector plant diseases like squash mosaic virus, which is present in Utah, though bacterial wilt has not been detected.

Symptoms include feeding scars on soft rinds of fruits (especially on the undersides), holes in stems and leaves, and destroyed flowers.

Monitoring is a critical part of any cucumber beetle management strategy. All above-ground parts of the plant, including the undersides of leaves and the bases of stems, should be checked regularly. Newly emerged or transplanted cucurbits should be scouted two to three times per week, as beetle feeding can rapidly kill small plants, while weekly scouting is sufficient for larger plants. When populations are high, utilize yellow sticky traps to aid in monitoring and control.

Read our full fact sheet on Cucumber Beetles.

Three-lined Potato Beetle

The three-lined potato beetle (Lema daturaphila) is a pest affecting many plants in the nightshade family, most notably tomatillos. Both adults and larvae can cause significant feeding damage to plant foliage.

Adults have orange bodies, black antennae, and two small black spots behind their heads. Their elytra (wing covers) are yellow with three black stripes running lengthwise down their backs. The larvae are yellow-green with blackheads and three pairs of legs, and they often cover themselves with their excrement as a defense against predators.

Three-lined potato beetles may overwinter in either the adult or pupal stage in the soil. They can emerge from May to August to mate and lay their eggs on host plants, with the eggs laid in groups on the undersides of leaves. After hatching, the larvae congregate and feed on foliage. Larvae pupate in mid to late summer, reaching the adult stage. In Utah, there is typically one generation per year.

Symptoms include holes within the foliage with severity based on population numbers.

Hand-removing the larvae and adults and placing them in soapy water can be effective for small-scale producers. Remove nearby weeds, especially those in the nightshade family, as they can serve as alternative hosts for the beetles. Row covers can be effective in excluding adult beetles when they emerge in the spring.

Read our full fact sheet on Three-lined Potato Beetles.

Colorado Potato Beetles

Adult Colorado potato beetles (Leptinotarsa decemlineata) have yellow and black stripes. Bright yellow to orange, oval-shaped eggs are laid in clusters of about 20-45 on the undersides of leaves. The larvae are reddish with bulbous-shaped bodies and two rows of black spots along their sides

Colorado potato beetles have 2-3 generations per season and are a concern from late April through potato vine-kill. They overwinter as adults under plant debris and in the soil, emerging around May. Larvae begin to feed on leaves in June, preferring the tops of plants. Begin scouting in mid-spring for signs of feeding damage or the presence of adults, eggs, or larvae.

Symptoms of their damage include notch wounds along the leaf margins, ragged injuries, and dark frass on the foliage. Both adults and larvae can cause significant harm to potato foliage.

Rotate crops to non-solanaceous varieties, keep the crop area free of solanaceous weeds, and apply insecticides as needed, rotating insecticide groups to manage resistance.

Asparagus and Spotted Asparagus Beetles

Monitor and manage asparagus beetles now to mitigate populations early next season when spears are being harvested.

Asparagus beetle (Crioceris asparagi) eggs are brown, oval, and individually cemented to asparagus plants, and can be distinguished from spotted asparagus beetle eggs by being attached on their end rather than their side. The larvae are plump and brown with a dark head capsule, chewing mouthparts, and three pairs of legs on the thorax, as well as fleshy prolegs near the hind end for grasping plants. Pupae resemble adults but have poorly developed wings and are yellow in color. Adults are brightly colored leaf beetles with bluish-black heads, antennae, and legs, and their forewings are typically bluish-black with three white spots and orange margins. When disturbed, adults are reluctant to fly and may drop from plants and “play dead” to evade predation.

Spotted asparagus beetle (Crioceris duodecimpunctata) eggs are brown or olive green, oval-shaped, and individually cemented to asparagus plants on their side. Larvae are plump with an orange to brown head capsule and chewing mouthparts. The pupa is yellow with poorly developed wings, resembling the adult. Adults are 6-8 mm long, mostly orange with black spots on the forewings, and black legs, eyes, antennae, and “knee caps.”

For both asparagus beetles and spotted asparagus beetles- Adults can consume leaves and scar spears and stems, with the most significant damage occurring in spring when they feed on new spears. While occasional summer damage can happen, it rarely affects growth or yield. Larvae feed on berries, which is usually not economically significant unless asparagus is grown for seed. Females cement eggs onto spears or ferns, causing aesthetic damage as the eggs are not easily washed away or removed.

Predatory beetles and parasitoid wasps will help keep populations to tolerable levels in most situations. Removing volunteer asparagus will prevent population spread over time. Minimizing weeds or other debris near asparagus will make sheltered areas less favorable for overwintering adults.

Read our full fact sheet on Asparagus and Spotted Asparagus Beetles.

Western Corn Rootworm

Adult Western corn rootworms (Diabrotica virgifera virgifera) are small beetles with yellow-green bodies and three black stripes on the forewings. Larvae are creamy white with a brown head capsule.

Western corn rootworms are active early June to mid-July. There is one generation per year. They overwinter as eggs in the soil. Monitor adults with yellow sticky traps; check and replace traps weekly.

Larvae feed with chewing mouthparts on roots causing browning, lesions, tunneling, curved cornstalks (goosenecking), yield losses, and susceptibility to root and stalk diseases. Adults feed with chewing mouthparts, resulting in poorly filled ears.

Larval feeding is the most damaging, while adult feeding typically does not result in economic loss. To manage the issue, rotate corn crops, plant early, and select varieties with vigorous root systems that are well adapted to the area.

Read our full fact sheet on Western Corn Rootworms.